references to external files dont work on all levels

Description

Depending on where a reference occurs, it is not resolved. This make modularization of distributed openapi spec files hard.

Swagger-codegen version

tested with 2.0.27, 2.0.23

Swagger declaration file content or url

worksnot.yaml:

openapi: 3.0.0
info:
  title: asdf
  description: |
    asdf
  contact: {}
  version: 0.0.0
servers:
- url: /v2
  description: server
paths:
  /works/worksnot:
    get:
      $ref: works_base.yaml#/paths/~1works~1/worksbase/get

works_base.yaml:

openapi: 3.0.0
info:
  title: asdf
  description: |
    asdf
  contact: {}
  version: 0.0.0
servers:
- url: /v2
  description: server
tags:
paths:
  /works/worksbase:
    get:
      summary: asdf

Command line used for generation

java -jar swagger-codegen-cli.jar generate -l openapi-yaml -i worksnot.yaml -o . -DoutputFile=works_r.yaml

Steps to reproduce

use above files and run comand line =>

works_r.yaml

openapi: 3.0.0
info:
  title: asdf
  description: |
    asdf
  contact: {}
  version: 0.0.0
servers:
- url: /v2
  description: server
paths:
  /works/worksnot:
    get: {}
components: {}

Start by reproducing the issue with worksnot.yaml, works_base.yaml, and the supplied java command, then inspect how external references are resolved during generation. Compare the working path-level $ref with references at other nesting levels. Done means external references resolve correctly in the generated works_r.yaml instead of producing an empty operation.